Front stage amplifier with different modes

ABSTRACT

A multimode front stage amplifier and method of amplifying a signal having an optimum signal output for weak signals as well as for strong signals provided for TV tuners. A product having a multimode front stage amplifier and provisions for selecting different modes of processing the signal.

FIELD OF THE INVENTION

The invention relates to amplifiers in general, and more specifically toamplifiers typically used in radio frequency (RF) receivers.

BACKGROUND OF THE INVENTION

Amplifiers are used for amplifying input RF signals to receivers such asTV tuners, multimedia tuners, and tuners for PCs.

Presently in a TV tuner (TV set), for example, there exist differenttypes of amplifiers, for example, a low-noise amplifier (LNA) typeamplifier with a bypass, or a power splitter type amplifier.

These two concepts have been used until today by most of the TV setmanufacturers, but both concepts have disadvantages. An LNA, forexample, with a high gain and low noise, is not able to handle normalcable TV signals, and a power splitter amplifier that is able to handlesuch signals has relatively high noise. These two drawbacks causeproblems, for example, when a TV set should be connectable to both acable TV system and a conventional antenna and at the same time providea high quality.

JP-A-10084500 describes a LNA for improved sensitivity especially forlow-level signals with a sensor for a certain threshold. The LNA can notbe used as a splitter for strong cable signals, for example, since thebypass suffers from implementation loss.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an amplifier that has anoptimum signal output for weak signals as well as for strong signals.

Herein, a “strong signal” denotes a signal having a strength comparableto a cable TV signal, a “weak signal” denotes a signal having a strengthcomparable to a signal from a conventional outdoor antenna.

The term “strong signal” typically refers to signals >1 mV, the term“medium signal” typically refers to signals >316 μV but <1 mV, and theterm “weak signal” typically refers to signals <316 μV. These values arenot absolute, but an example. Signal values that are outside theselimits but have a similar size are also within the scope of theinvention as defined in the claims.

According to a first aspect of the invention, the object is obtained bya multi-mode amplifier that can be switched between high gain in case ofa weak signal and low gain in case of a strong signal.

In this way, the amplifier can have different characteristics fordifferent signals; this is of great importance in particular for hybridanalog/digital tuners.

According to a preferred embodiment of the invention, there is providedan amplifier device, the amplifier device comprising:

-   -   amplifier means for amplifying a radio frequency (RF) input        signal, and    -   a controllable feedback loop for adjusting a gain and a bias        voltage applied to the amplifier means for adjusting a current        determining a noise level, arranged to provide at least two        different modes, a first mode providing high gain and low noise        for handling weak signals and a second mode providing low-gain        power splitting for handling strong signals. The mode can be        selected independence on the input signal received, which will        result in an optimum signal output.

Preferably, the amplifier device comprises a mode selection means, andthe feedback loop connected between an output and an input of theamplifier means comprises at least two resistors a first resistor and asecond resistor connected in parallel to each other, wherein the secondresistor is connected in series with a switch controlled by the modeselection means, which mode selection means also controls a bias voltageapplied to the amplifier means. This is a cost-effective solution whentwo modes are required to deliver optimum signal outputs depending onwhether a strong or a weak input signal is received. The mode selectionmeans comprises circuitry for selecting between the at least twodifferent modes.

Preferably, the mode selection means control the feedback loop and thebias voltage to provide a third mode providing high gain and highcurrent. This third mode delivers an optimum signal output whenreceiving a medium-level input signal.

According to another embodiment of the invention, a product is providedcomprising the amplifier device and provisions for selecting the modes.In this case the optimum signal outputs of the amplifier device in theproduct may be selected manually or automatically.

According to another preferred embodiment of the invention, a method ofamplifying a radio frequency (RF) signal is provided comprising thesteps of:

-   -   amplifying the signal in at least a first mode and a second mode        by amplifier means having at least two modes, said first mode        providing high gain and low noise for weak signals, and said        second mode providing low gain for handling strong signals.

Preferably, the method further comprises the step of:

-   -   amplifying the signal in a third mode, said third mode providing        high gain and high current for medium signals.

These and other aspects and embodiments of the invention will beapparent from the preferred embodiments(s) described hereinafter.

BRIEF DESCRIPTION OF THE-DRAWINGS

The present invention will be more clearly understood from the followingdescription of the preferred embodiments of the invention read inconjunction with the attached drawings, in which:

FIG. 1 is a circuit diagram showing an amplifier device according to apreferred embodiment of the invention.

FIG. 2 is a graph showing how the amplifier device in FIG. 1 operates ina splitter mode.

FIG. 3 is a graph showing how the amplifier device in FIG. 1 operates inan LNA mode.

FIG. 4 is a flow chart illustrating a method according a preferredembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a circuit diagram of an amplifier device 10 according to apreferred embodiment of the invention. The amplifier device 10 comprisesan operational amplifier 1 having an output 1 a for delivering aradio-frequency output signal RFout connected in a feedback loop 1 c toan input 1 b of the amplifier 1 for receiving a radio-frequency inputsignal RFin. The feedback loop 1 c comprises two different resistors, afirst resistor R1 and a second resistor R2 connected in parallel to eachother, which resistors R1 and R2 can be connected in different ways bymeans of a first switch SW1 connected in series with one of theresistors R1 and R2, in this case the second resistor R2. The firstswitch SW1 is shown in an OFF position, corresponding to an LNA mode.The amplifier device 10 further comprises two resistors controlling thebias of the operational amplifier 1, i.e. a third resistor R3 coupled toa voltage Vbias and a fourth resistor R4 connected to ground, bothcoupled to the amplifier 1 (at the same terminal). The fourth resistorR4 is controlled by means of a second switch SW 2 connected in serieswith the fourth resistor R4.

The amplifier device (10) can be used as a device coupled to a tunerinput or as an improved splitter arranged to supply output signals to atleast two tuners.

When the amplifier device 10 operates in the LNA mode, the second switchSW2 is ON. The operational curve is shown in FIG. 2 showing gain G andnoise figure NF plotted versus frequency f. When operating in the powersplitter mode, the first switch SW1 is ON and the second switch SW2 isOFF. The curve of this mode is illustrated in FIG. 3, where gain G andnoise figure NF are plotted versus frequency f.

The first and second switches SW1 and SW2 are controlled by a modeselection means 15.

A third mode is achieved when both switches SW1 and SW2 are OFF, wherebya high gain splitter and high current LNA is obtained at the same time.This third mode is intended for a medium-strength signal.

The mode selection means 15 can be controlled by a button on a remotecontrol device or via another switch on the amplifier device (15) or ona product in which the amplifier device (15) is present. The modeselection means 15 may also be arranged to be controlled automaticallyby using an output of a signal to noise ratio detector as can be foundin IF-processors.

As described, an LNA tuner of today is not always able to handle signalsoffered by a cable TV system and therefore requires a bypass. Due toimplementation losses, it suffers an overall deterioration in systemperformance anywhere from −1 dB (at 50 MHz) to −3 dB (at 860 MHz). Byswitching this LNA to the splitter mode, which is accomplished by modeselection means 15 controlling the switches SW1 and SW2 (indicated bydashed lines in FIG. 1), the amplifier device 10 is also able to handlethese cable TV signals without any loss in system performance comparedto a “normal” tuner.

In the LNA mode, a receiver (not shown) coupled to the output of theamplifier device 10 is able to achieve good noise properties (typicallylow noise) and high gain.

In the splitter mode, a receiver (not shown) does not suffer from anydegradation due to the lower gain of the amplifier device (10) since itis operating in the splitter mode. The wide input stage will give theamplifier device (10) the same intermodulation limitation as a splitter.

In the third mode, the gain of the amplifier device is increased whilekeeping the current high for an intermodulation level between the levelof a splitter and the LNA mode. The overall system signal to noise (S/N)performance is improved thereby.

A typical performance for an amplifier device according to the inventionis: LNA mode: RF-IF NF 3 dB, gain >50 dB Splitter mode with RF out:RF-IF NF 8 dB, gain >40 dB

The invention may also be realized in a method, which will be describedbelow with reference to FIG. 4.

A first step 101 comprises amplifying the signal in at least a firstmode and a second mode by amplifier means having at least two modes,said first mode providing high gain and low noise for weak signals, andsaid second mode providing low gain power splitting for handling strongsignals.

A second step 102 comprises amplifying the signal in a third mode, saidthird mode providing high gain and high current for medium signals.

The invention finds its application, for example, in handling cable,terrestrial, and satellite TV signals.

As used in the following claims, it should be noted that theabove-mentioned embodiments illustrate rather than limit the invention,and that those skilled in the art will be able to design manyalternative embodiments without departing from the scope of the appendedclaims. In the claims, any reference signs placed between parenthesesshall not be construed as limiting the claim. The verb “comprise” in allits conjugations does not exclude the presence of elements or stepsother than those listed in a claim. The word “a” or “an” preceding anelement does not exclude the presence of a plurality of such elements.The invention can be implemented by means of hardware comprising severaldistinct elements, and by means of a suitably programmed computer. Inthe device claim enumerating several means, several of these means canbe embodied by one and the same item of hardware. The mere fact thatcertain measures are recited in mutually different dependent claims doesnot indicate that a combination of these measures cannot be used toadvantage. (See above).

1. An amplifier device (10), said amplifier device comprising: amplifier(1) means for amplifying a radio-frequency input signal RFin, acontrollable feedback loop (1 c) for adjusting a gain and a bias voltageapplied to the amplifier means (1) for adjusting a current determining anoise level, the feedback loop and the bias voltage being arranged toprovide at least two different modes, a first mode providing high gainand low noise for handling weak signals and a second mode providinglow-gain power splitting for handling strong signals.
 2. An amplifierdevice (10) as claimed in claim 1, wherein the amplifier device (10)comprises mode selection means (15), and the feedback loop (1 c) isconnected between an output (1 a) and an input (1 b) of the amplifiermeans (1), the feedback loop (1 c) comprising at least a first resistor(1) and a second resistor (R2) connected in parallel to each other, andwherein the second resistor (R2) is connected in series with a switch(SW1) controlled by the mode selection means (15), which also controlthe bias voltage applied to the amplifier means (1).
 3. An amplifierdevice (10) as claimed in claim 1, wherein the mode selection means (15)are arranged to control the feedback loop (1 c) and the bias voltage toprovide a third mode providing high gain and high current.
 4. A productcomprising the amplifier device (10) as claimed in claim 1 and means forselecting the at least two different modes.
 5. A method of amplifying aradio-frequency signal, the method comprising the step of: amplifyingthe signal in at least a first mode and a second mode by amplifier meanshaving at least two modes, said first mode providing high gain and lownoise for weak signals, and said second mode providing low-gain powersplitting for handling strong signals.
 6. A method as claimed in claim5, further comprising the step of: amplifying the signal in a thirdmode, said third mode providing high gain and high current for mediumsignals.